In general, this invention relates to camera shutter arrangements; more particularly, it relates to a control circuit therefor which enables manual adjustment of the exposure time of the shutter.
Prior art manual shutter control circuits determine the exposure time depending on the time constant of a series circuit consisting of a capacitor and a variable resistor. It is known, however, that the control circuits of this type involve several disadvantages. The variable resistor can provide only a reduced adjustment accuracy in a low resistance area and hence the control circuit of this type presents an unsatisfactory voltage variation characteristic at low voltages. Furthermore, when it is required to control the shutter time over a wide range, the manual shutter control resistor has to be of such a type that can be varied over a wide range, from a very high resistance value to a very low resistance value. As is well known, it is difficult to manufacture such a resistor. Still another disadvantage involved in the prior art control circuit is that, when semiconductor devices are used, the construction of the circuit becomes complicated and that difficulties are encountered in providing a control circuit having good temperature characteristics because of the cumulative influence of the ambient temperature over the semiconductor devices used.